Depth-structured diversity: high number of undescribed species of Tanaidacea (Crustacea) across depth gradient in subarctic regions of the NE Pacific

This study investigated the diversity and ecological structuring of deep-sea tanaidacean assemblages across four environmentally distinct regions of the North Pacific: the Bering Sea, the Aleutian Trench, and its northern and southern slopes. Sampling was conducted during the AleutBio (SO293) expedition aboard RV Sonne in 2023 using standardized benthic gear, including the epibenthic sledge (25 valid deployments) and box corer (11 valid deployments), at depths ranging from 3,500 to 7,200 m. Each region encompassed a unique deep-sea setting, characterized by specific bathymetric profiles, geomorphological features, and presumed trophic regimes. A detailed morphological analysis identified 63 morphospecies, of which 62 are likely undescribed. Species richness declined with increasing depth and reached its highest levels in the Bering Sea. Beta diversity analyses revealed significant differences in community composition among regions, primarily driven by depth, and secondarily by food availability, inferred from dissolved silica concentrations.